1. Field of the Invention
The present invention relates to a colored composition used for manufacturing a color filter and a black matrix included in, for example, a color liquid crystal display device and a color image pick-up tube device, to a method of manufacturing a color filter using such a colored composition, and to a method of manufacturing a black matrix using such a colored composition.
2. Description of the Related Art
In the manufacture of a color filter included in a liquid crystal display (LCD) device, it is necessary to form a uniform film of coating having a thickness of about 1 to 3 μm after drying, by coating a coating liquid on a transparent substrate. In general, a spin coating method is employed in the coating step.
The spin coating method is a coating method in which a coating liquid is applied dropwise onto a transparent substrate while rotating the transparent substrate at a prescribed rotating speed so as to cause the applied coating liquid to be spread centrifugally on the surface of the transparent substrate, forming a film of coating having a thickness which is determined by, for example, the viscosity of the coating liquid and the rotating speed of the transparent substrate.
The spin coating method includes an open-to-air system and a closed cup system. Each of these systems is disadvantageous in that the film of coating is rendered nonuniform in thickness in the radial direction of the transparent substrate such that the film is rendered thicker in the central portion about which the transparent substrate is rotated and in the peripheral portion than in the intermediate portion. A coating composition that permits overcoming the disadvantage noted above is disclosed in, for example, Japanese Patent Disclosure (Kokai) No. 6-3521. The disclosed coating composition contains a pigment, a binder polymer and a radiation-sensitive compound, dissolved or dispersed in a specified organic solvent. This composition, when applied by the spin coating method, permits diminishing the difference in thickness of the film of coating between the central portion and the peripheral portion of the transparent substrate and also permits forming a film excellent in its surface smoothness.
The coating composition noted above certainly permits diminishing the nonuniformity in thickness of the film. However, the spin coating method in general is disadvantageous in that only several percent of a coating liquid applied onto a transparent substrate is utilized for the formation of the film on the transparent substrate, and the remaining coating liquid exceeding 90% scatters out of the transparent substrate, which is wasteful. The waste of a large amount of the coating liquid constitutes nowadays a serious problem with increase in the substrate size.
As a measure for overcoming the above-noted disadvantages inherent in the spin coating method, a die coating method is being studied in recent years as disclosed in, for example, Japanese Patent Disclosure Nos. 7-168015, 2000-193818 and 2001-195004. The die coating method is advantageous in that the. waste of the coating liquid can be suppressed, compared with the spin coating method, and that the supply circuit of the coating liquid including the tip of the coating head forms a closed system.
In the die coating method, however, the coating liquid is exposed to the atmospheric air at the open portion of the slit at the tip of the coating head, with the result that the coating liquid tends to be dried and solidified at the tip of the coating head. It follows that the solidified material of the coating liquid causes the plugging of the slit forming the nozzle and causes the film formed on a glass plate to bear streaks extending in the coating direction. Further, the solidified material of the coating liquid may be released from the tip portion of the coating head so as to be mixed as a foreign matter with the film formed on the glass plate so as to deteriorate the film. Further, where such a defect has been generated, it is necessary in many cases to detach the coating head from the coating apparatus so as to dismantle and clean the coating head. The operation to dismantle and clean the coating head takes a considerably long time, with the result that the reduction in time efficiency of the coating apparatus is not negligibly small.
It is difficult to overcome the difficulty noted above by simply using in the die coating method a composition adapted for use in the spin coating method.